1. Field of the Invention
The present invention relates to rotational angle sensors. The present invention also relates to throttle devices having the rotational angle sensors.
2. Description of the Related Art
Japanese Laid-Open Patent Publication No. 2005-48671 teaches a known throttle device that is operable to control an amount of flow of intake air that is supplied to an engine of an automobile. The throttle device includes a throttle valve for controlling a degree of opening of an intake air channel depending on the rotational angle of the throttle valve. Magnets are attached to an end portion of a shaft of the throttle valve. A rotational angle sensor having a magnetoresistive element is operable to detect the change of direction of the magnetic field produced by the magnets. The magnetoresistive element is integrated with a cover member by an insertion molding process. The cover member is adapted to cover a drive mechanism for rotatably driving the throttle valve.
The magnetoresistive element of the throttle device of this publication is integrated with the cover member by an insert molding process. Therefore, there is a possibility that the magnetoresistive element, in particular a chip constituting a sensing section, may be damaged by the molding pressure during the molding process. In addition, the chip of the magnetoresistive element may be deformed to cause deflection by the stress that may be produced due to contraction of a molded resin after the molding process. As a result, output characteristics of the magnetoresistive element may be degraded. The output characteristics may include the linearity of output and the output drift that may be caused due to change in temperature.
International Publication WO 2004/031558 teaches another known throttle device that is operable to control an amount of flow of intake air supplied to an engine of an automobile. Similar to the above known throttle device, the throttle device of this publication includes a throttle valve for controlling a degree of opening of an intake air channel depending on the rotational angle of the throttle valve. Magnets are attached to an end portion of a shaft of the throttle valve. A rotational angle sensor having a magnetoresistive element is operable to detect the change of direction of the magnetic field produced by the magnets. The magnetoresistive element has connecting terminals connected to plate-like terminal members, so that substantially the entire magnetoresistive element including a sensing section extends in an upright manner from the terminal members. The terminal members supporting the magnetoresistive element are disposed within a housing. The magnetoresistive element is loosely received within a depression formed in the housing
With this known throttle control device, substantially the entire magnetoresistive element including the sensing section extends in an upright manner from the terminal members and is positioned within the depression of the housing. Therefore, the position of the magnetoresistive element tends to become unstable. For example, the sensing section of the magnetoresistive element may vibrate due to external vibrations, such as vibrations of the engine and vibrations of the vehicle body that may be caused during traveling of the vehicle. When the sensing section vibrates, the sensing section may move from a proper position determined relative to the magnets. As a result, output characteristics of the magnetoresistive element may be degraded.
Therefore, there is a need in the art for a rotational angle sensor that can prevent or minimize degradation of the output characteristics. Also, there is a need in the art for a throttle device having such a rotational angle sensor.